What particle sizes must surgical masks filter to meet the FDA's Covid-19 guidance for face masks?
The FDA's Covid-19 guidance for surgical masks states that manufacturers cannot make "filtration claims" for particles of any size and cannot label them "for antimicrobial or antiviral protection." The FDA also states that "a surgical mask is meant to help block large-particle droplets, splashes, sprays, or splatter...." In contrast, the bulk of Covid-19 transmission occurs via microscopic aerosols that are below 1 micron in diameter. A study published in 2003 by the Journal of Textile and Apparel, Technology, and Management studied six different types of surgical masks and found that their average pore sizes ranged from 17 to 51 microns, and their max pore sizes ranged from 27 to 147 microns. Collectively, these pore sizes are at least 17 to 147 times larger than 90% of the virus-carrying aerosols exhaled by people infected with C-19.